Miniature gas turbine or turbojet engines, typically of 150 lb-f thrust and smaller, are often useful for single-use airborne applications such as reconnaissance drones and other unmanned air and ground launched aeronautical vehicles. The use of such an engine greatly extends the range of such vehicles in comparison to the more conventional solid fuel rocket engine.
A miniature gas turbine engine must have a relatively inexpensive manufacturing cost coupled with a high degree of starting and operational reliability when launched from air or ground systems in order to be an economically feasible extended range expendable propulsion source for such applications. The high-speed ball bearings in a bearing system that support the rotating turbine machine are one type of component that greatly affects mechanical performance and reliability of a miniature gas turbine engine. Reliability and efficiency of the bearings in the bearing system are prime concerns for a successful expendable turbine engine. The most common cause of reduced reliability and efficiency of an expendable turbine engine bearing system is poor or inadequate lubrication of the bearings.
Although bearing systems for large reusable provide satisfactory reliability and efficiency, they employ a relatively complex closed circuit lubrication system that is relatively expensive to manufacture and difficult to maintain under the long term storage conditions needed for typical single use miniature gas turbine engines. Accordingly, it is desirable to achieve bearing lubrication with the reliability and efficiency of large turbine engines in an uncomplicated and inexpensive bearing lubrication system for a miniature gas turbine engine that assures a similar degree of operational efficiency and reliability.